Water and Sewers

What is inflow and infiltration

Inflow and Infiltration refers to rainwater and groundwater that enters the sanitary sewer through a variety of defects.

Inflow sources allow rainwater to enter the sanitary sewer directly from the surface through improper plumbing and cross connections. Some examples include downspout and roof drain connections, and catchbasin cross connections.

Infiltration sources allows the groundwater to seep into the sanitary sewer through cracks or bad joints in sewer pipes and manholes.

A certain amount of inflow and infiltration is unavoidable and is accounted for in routine sewer design. However, when inflow and infiltration exceeds design allowances, sewer capacity is consumed and may result in overflows, risks to health, damage to the environment and increased treatment and disposal costs.

Inflow and infiltration reduction: Why bother?

Inflow and infiltration sources allow large volumes of clean water into the sanitary sewer system that generally were not designed to handle such volumes. Most of the sanitary network in Peterborough was designed and constructed in 1960s. Many older pipes simply don't have the capacity to deal with the volume of wastewater that now courses through them. Stormwater entering the sanitary sewers, especially in the older parts of the City, overwhelms the sewers. Sewer overload is a frequent cause of basement flooding, which is very expensive and disruptive for those affected. It may also result in sewage surcharge into the lake and rivers. This is a potential reason for the beach closing, and also causes pollution to fish and wildlife. In addition, climate change has been increasing the magnitude of storms and flooding.

Municipal attempts to prevent flooding and sewer overflows can be enormously expensive. The cost to reduce flooding in a single low-lying area could be hundreds of millions of dollars and take many years to complete. In comparison, inflow and infiltration reduction is cost effective, helps immediately, and even reduces operational and treatment costs at the Wastewater Treatment Plant. The benefits of inflow and infiltration reduction has been proven in practice in various municipalities and is strongly recommended by various private and public parties.

How does the inflow and infiltration reduction project work?

The City of Peterborough initiated the Infiltration and Inflow Reduction Program in April 2014. The project objective is to identify and remediate sources of extraneous flow into the sanitary system (also known as inflow and infiltration sources). Three main steps of the project are:

1. Source Identification;
2. Communication; and,
3. Remediation.

Step 1 is typically performed by the City although the landowner can identify suspected inflow and infiltration sources on their own property and inform the City. Step 2 is performed by the City. Step 3 is performed by the landowners, however funding may be available through the subsidy program.

All of the Environmental Protection operating expenses, except the Little Lake Fountain, plus Public Works Sanitary Sewer maintenance costs, are funded through Sewer Surcharge Revenues. The revenue from “extra strength” surcharge agreements, and hauled sewage from surrounding counties, will continue to offset operating costs.

All of the Environmental Protection Capital works, plus Wastewater Related Capital works, are funded either through contributions from the Waste Water Reserve Fund or through Development Charges.

Sewer surcharge rates – past years

2023: 104.46% of eligible water charges

2022: 102.92% of eligible water charges

2021: 102.92% of eligible water charges

2020: 101.9% of eligible water charges

2019: 99.14% of eligible water charges

2018: 97.08% of eligible water charges